The neighborhood is named after the town of Dorchester in the English county of Dorset, from which Puritans emigrated on the ship Mary and John, among others and is today sometimes nicknamed "Dot" by its residents.

Dorchester, now covering a geographic area approximately equivalent to nearby Cambridge, was founded in 1630 just a few months before the founding of the city of Boston. It was still a primarily rural town and had a population of 12,000 when it was annexed to Boston in 1870. Railroad and streetcar lines brought rapid growth, increasing the population to 150,000 by 1920. In the 2010 United States Census, the population was 92,115. Dorchester as a separate municipality would rank among the top five Massachusetts cities.